The present invention relates to improved sheet handling systems for copiers, and in particular to an improved sheet stacker and normal force applicator.
As xerographic and other copiers increase in speed, and become more automated, it is increasingly important to provide higher speed yet more reliable automatic handling of both the copy sheets and the individual original documents being copied. Yet, it is desired to accommodate original documents and copy sheets which vary widely in size, weight, thickness, material, condition, humidity, age, etc.. It is desirable to automaticaly handle such individual document or copy sheets in rapid succession with relatively compact and inexpensive sheet handling apparatus. Further, it is desirable to provide sheet handling apparatus which accommodates different sheet orientations and movement directions so as to be able to optimize and compact the design of the copier and/or its document handling unit.
A particularly difficult sheet handling problem is the separation and feeding of individual sheets from the bottom of a set of stacked, unseparated, sheets. This difficulty in the sequential feeding of individual bottom sheets from a stack by a bottom sheet feeder is greatly compounded when it is also desired to be able to restack additional sheets on top of the same stack during the same copier operations in which sheets are being withdrawn from the bottom of that stack.
A particularly desirable type of sheet separator and feeder is the retard type described in U.S. Pat. No. 3,768,803, issued Oct. 30, 1973, to K. K. Stange, and other references cited herein. However, particularly with a light weight or variable height stack of sheets, this and various other types of sheet feeders often require a normal force applicator for fully reliable bottom sheet feeding. This can be a weighted or spring loaded plate or bail bar or the like. The normal force applicator presses down on the top of the stack of sheets to hold down the stack and provide a sufficient engagement force between the bottom-most sheet of the stack and the bottom feeder.
A serious disadvantage of most known normal force applicators is that by their engagement of the top of the stack of sheets they block or interfere with the stacking of additional sheets onto the top of the stack. Conventionally the normal force applicator is intermittently lifted off of the top of the stack each time it is desired to stack additional sheets thereon manually or automatically. However, that has a serious disadvantage of interrupting the continued application of the normal force needed by the bottom feeder. That is, the normal force is removed during the time period in which an incoming top sheet is being stacked, i.e., slid forward under the raised normal force applicator into alignment with the front stack stop. Thus, bottom feeding with an applied normal force cannot be conducted simultaneously with the stacking of sheets on top of the same stack in such systems. Further, if the normal force applicator is lifted automatically each time a sheet is loaded onto the stack an additional mechanical or electromechanical system must be provided for this intermittent lifting movement and normal force application.
In contrast, the present invention is a low-cost, simple system for providing both an effective and desirable normal force application to the top of the stack without the above-noted disadvantages and also providing, with the same unit, an effective sheet restacking (jogging) system. The present system is capable of simultaneously and continuously applying an effective normal force to the top of widely variable size stacks for a bottom retard sheet feeder, while also jogging individual sheets being continuously restacked on the top of the stack into alignment with a front stack on the top of the stack into alignment with a front stack stop. Thus, sheets may be restacked simultaneously with the feeding of the bottom sheet of the stack with the normal force applied.
A particularly important known application of bottom feeding/top restacking sheet separating and feeding systems is in pre-collation copying systems where a stacked set of original documents must be multiply recirculated without damage to and from the stack of documents. Some examples of art relating to pre-collation document handling systems in which a document is withdrawn from the bottom of a document set stack for copying and then returned to the top of the stack include: U.S. Pats. No. Re. 27,976, (originally U.S. Pat. No. 3,499,710, issued Mar. 10, 1970, to L. W. Sahley); U.S. Pat. No. 3,552,739, issued Jan. 5, 1971, to R. R. Roberts, et al.; U.S. Pat. No. 3,536,320, issued Oct. 27, 1970, to D. R. Derby; U.S. Pat. No. 3,556,511, issued Jan. 19, 1971, to A. Howard, et al.; and U.S. Pat. No. 3,937,454, issued Feb. 10, 1976, to R. H. Colwill. A recent pre-collation copying system of this type is shown in Belgium Pat. No. 835,568 laid open May 13, 1976, and West German patent application No. 2,550,985 published May 26, 1976, and French application Publication No. 2,291,131, laid open Nov. 12, 1976, all based on U.S. application Ser. No. 523,610, filed Nov. 13, 1974 now abandoned. A disclosure similar to the latter is in U.S. Defensive Publication T957,006 of Apr. 5, 1977, based on application Ser. No. 671,865, filed Mar. 30, 1976, by M. G. Reid, et al..
The systems shown in these latter two applications are also of interest as examples of the use of foraminous sheet feeding rollers and rear stack joggers. They also disclose other features of interest to the present application.
A preferred example of a copier control system and logic circuitry in which the systems disclosed herein may be incorporated is described in U.S. Pat. No. 3,936,182, issued Feb. 3, 1976, to Sikander Sheikh. Accordingly, that patent is also incorporated herein. While integral software incorporation into the copier's general logic circuitry and software, as in that patent, of the functions and logic defined herein is preferred, the invention may be conventionally incorporated into a copier utilizing any other suitable software or hard wired logic system or microprocessor.
An example of a stacking tray with a bottom retard sheet feeder and a normal force applicator therefor is disclosed in U.S. Pat. No. 4,014,537, issued Mar. 29, 1977, to K. K. Stange. Bottom air flotation (which to a certain extend will affect the normal force requirements) is also disclosed there.
The use of a foraminous impact or bounce pad for reversing the direction of motion of a sheet in a duplexing system is shown in U.S. Pat. No. 3,856,295, issued Dec. 24, 1974 to John H. Looney.
In regard to the use of a continuously rotating jogging or stacking member to compile sheets in a stack against a registration edge there is noted by way of example a U.S. Pat. No. 3,709,595, issued Jan. 9, 1973, to L. H. Turner, et al..
All of the patents cited herein for art purposes are also incorporated by reference herein to the extend they provide teachings of usable or alternative systems or hardware for the disclosed embodiments herein.